Random bred hamsters infected with Dipetalonema viteae exhibit two resistance mechanisms: Microfilariae from a primary infection are eliminated from the bloodstream 100-120 days postinfection - no microfilaremia results from subsequent infections; hamsters given repeated infections respond to adult worms by encapsulating them in the subcutis. One strain of inbred hamsters investigated does not terminate blood microfilaremia. Infection in other inbred strains of hamsters is being investigated. Immunologic mechanism for both phenomena merit study. An integral part of such studies is use of purified parasite antigen in tests of humoral and cellular immunity. Soluble somatic, membraneous and metabolic antigens from larval and adult stages of the parasite are fractionated by isoelectric-focusing in sucrose gradients and polyacrylamide gels. The membraneous antigen preparations are solubilized with detergents prior to isoelectric-focusing. The sensitivity of immunologic tests has been increased by labeling purified antigens with isotopes. Use of infective larvae permanently tagged with radioactive labels should determine which of a series of larval infections yield adult worms susceptible to encapsulation in the resistant host. Feasibility of vaccinating hamsters with combinations of purified parasite antigens is planned. This vaccination method is being compared with a method using larvae attenuated by irradiation. BIBLIOGRAPHIC REFERENCES: Neilson, J. T. M. Failure to vaccinate lambs against Haemonchus contortus with functional metabolic antigens identified by immunoelectrophoresis. Int. J. Parasitol. 5:427-430, 1975. Neilson, J. T. M. and D. J. Forrester. Dipetalonema viteae: Primary, secondary, and tertiary infections in hamsters. Exptl. Parasitol. 37:367-372, 1975.